1. Field of the Invention
The present invention relates to a liquid discharge apparatus and an inkjet recording apparatus, and more particularly to a structure for a discharge head suitable for realizing a stable liquid discharge and a technology of drive control thereof.
2. Description of the Related Art
Inkjet recording apparatuses deposit ink droplets on a recording medium by relatively moving recording paper or another recording medium with respect to a recording head provided with ink discharge nozzles while discharging ink from the recording head in accordance with a print signal, and an image is formed on the printing medium by the ink dots. The inkjet recording apparatuses stop discharging ink or experience other discharge defects when the viscosity of the ink increases inside the nozzles due to drying or the like. The resupply performance (refill performance) of ink to the nozzles is reduced when the ink viscosity increases.
In view of the above, Japanese Patent Application Publication No. 11-10878, in a so-called thermal-jet (side shooter, in particular) inkjet printing apparatus in which a thermal-expansion heater for generating the thermal energy required for discharge is disposed in an ink flow channel, proposes technology for improving the discharge and refill performance by disposing a first thermal heater in a position near the discharge port inside the ink flow channel, disposing a second thermal heater in a position farther from the discharge port than the thermal-expansion heater, and controlling the viscosity of the ink by means of these two thermal heaters.
Japanese Patent Application Publication No. 6-91893 discloses an inkjet printer provided with a head heater for heating the entire head, and an ink chamber heater for heating each ink chamber individually.
The method proposed in Japanese Patent Application Publication No. 6-91893 focuses on the ink temperature in the discharge direction and controls the viscosity and volume of the ink, but in accordance with this method, the entire head must be warmed in order to obtain liquid properties that are adequate for discharge, so a considerable amount of energy is required. In particular, initial heating is required from power-on until the first printing operation is possible.
In accordance with the method disclosed in Japanese Patent Application Publication No. 11-10878 concerning this point, the entire head is not required to be heated because the structure provides thermal heater to individual flow channels. Nevertheless, the method proposed in Japanese Patent Application Publication No. 11-10878 has a structure in which thermal heaters are disposed in close proximity at intervals of several tens of micrometers on the discharge side and supply side with respect to the ink flow channel in the same plane, so there is a drawback in that as the number of discharges increases, the temperature difference between these two heaters grows smaller, and the effect of higher discharge strength is lessened. Furthermore, the structure disclosed in Japanese Patent Application Publication No. 11-10878 is a discharge type that uses expansion produced by thermal resistors, and has a thermal-expansion heater for high temperature heating that is more powerful than a thermal heater. The thermal heater is disposed in a very close positional relationship forward and rearward of this heater, so there is a drawback in that the temperature difference between the heaters is even smaller.